The process for producing an acrylic acid via a catalytic gas phase oxidation process, an absorption and/or a condensation process , and further a distillation purification and/or a crystallization process has been industrially performed widely. Purified acrylic acid is transferred and stored in a storage tank, and if a trace of acrylic acid polymer is contained in the purified acrylic acid, an acrylic acid polymer will be further generated during storage, and problems such as the decreasing of purity of the purified acrylic acid are caused.
In order to solve the above problems, the present inventors have previously proposed a method for filtering with a filter when the purified acrylic acid is transferred to a storage tank. (Refer to patent document 1). In said method, in order to remove the acrylic acid polymer adhered to the used filter, the filter was washed with aqueous sodium hydroxide solution after water washing, and further water washing was carried out.
The acrylic acid polymer adhered on the filter can be substantially removed by washing with water and aqueous sodium hydroxide solution, and performing further water washing as described in the above patent document 1. It should be noted that a final water washing is performed for removing the alkaline residues which remain on the filter after washing with aqueous sodium hydroxide solution.